Engraved printing rolls of the modern type are cylindrical in shape. Engraved on the cylindrical surface are a large number of cavities designed to hold ink which will be deposited on the desired printing medium, for example, paper, fabric, or plastic. The engraved cavities are called "cells" in the industry, and several hundred such cells or recesses are formed per linear inch; their depth may range from about 0.0015 inches to about 0.0008 inches.
The general operating characteristics of a printing operation of the type being considered in this invention are disclosed in the patent to Heurich, U.S. Pat. No. 3,613,578, and to the extent necessary for an understanding of the operation such is incorporated herein by reference.
The earliest form of engraved printing roll had a pattern of circular shaped cells. This produced a substantial "corner post" between the cells. In the industry a "corner post" is the area between cells where ink will not print, for example, with four cells in a square pattern the "corner post" is the flat area at the center of the square where no ink will be deposited.
Subsequently square shaped and hexagon shaped cells were developed. This obviously served to reduce the size of the corner post.
Another development included tri-helical grooving. This further reduced "corner post" problems but suffered the side effect of causing lateral ink migration with less control over the coating application.
So called "electronic engraving" (where a detector "reads" a black and white print of a design pattern to control a cutting stylus) can be programmed so that the stylus drags between one cell and the next to create a relatively shallow interconnecting channel; this aids the flow of ink. There is also known (see U.S. Pat. No. 4,301,583) a mechanical engraving process in which a shallow V-cut channel exists between adjacent cells.
A patent to Hieber et al (U.S. Pat. No. 4,155,766) shows a screen for engraving having interconnection of cells via channels which is another way the prior art has tried to improve the engraving procedure, to reduce the corner post and improve the resulting printing.